Fallback_splitsize of 100 MB < 0.1% of tape length

This article is for Amanda Enterprise (AE) v. 3.1.5

Link to more info: http://wiki.zmanda.com/index.php/Splitsize_too_small

Issue Symptoms

The below message is shown as a warning in ZMC or when running amcheck from command line:

"fallback_splitsize of 100 MB < 0.1% of tape length"

Issue Description

The fallback_splitsize is an Amanda device parameter in versions 3.1.5 and earlier that specifies the amount of data to cache in RAM when more than one tape is allowed per backup and for times when the backup is not written to the staging area first.  Normally, backups are split in the staging area before going to tape but, when a backup is not written to the staging area first, it is split in RAM instead and should not be less than 1% of the size of the backup.  As Amanda does not know how large the size of the backups will be during the host check, the user is alerted if the split size is particularly small compared to the tape size.

Resolution

To resolve this, edit the YAML file for the changer profile in directory /etc/zmanda/zmc_aee/device_profiles/ and find the line that reads

fallback_splitsize: 100m

Change the conservative default of 100m to a number that is at least 1% of the size of your largest backup or, if unknown, at least 0.1% the size of your tape.  This data size is cached in RAM so you must have sufficient RAM for the specified amount of data and should not exceed 3.5G.The change will be made for all backup sets that use this changer device.

After making this change, navigate to the Admin|backup sets page in the Zmanda Management Console to have the change take effect.

If there is not sufficient available RAM to specify the desired or needed split size, Amanda can be configured to split the backup on disk instead of RAM.  Contact support to get help with configuring this.

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